PLEASANTON — State Parks officials presented their preferred concept for a 3,500-acre expansion of the Carnegie State Vehicular Recreation Area on Tuesday, calling for a system of more multiuse off-highway trails, camping, and parking areas in a hotly debated area southeast of Livermore.

The area now has about 1,600 acres of riding areas.

Nearly 350 environmentalists and off-highway enthusiasts packed the meeting room at Amador Valley High School to view and comment on conceptual maps for the state-managed off-highway park.

The plans show expanded areas for use by four-wheel drive trucks, all-terrain vehicles, four-seaters and motorcycle riding trails, as well as gathering and practice areas. Planners hatched the concept by incorporating parts of three alternatives, along with public comments and stakeholder meetings, patterning it after similar land use at the Hollister Hills SVRA south of Hollister.

“It’s a model we think will work here,” said State Parks’ sector superintendent Randy Caldera, who oversees Carnegie. “From my perspective, we’ve hit a home run. … We worked a lot of hours on this.”

The plan also includes an interpretive center at the site of the abandoned coal mining town of Tesla.

But the possibility of opening up an area that includes the remnants of Tesla has upset members of a coalition of about 20 environmental groups called Friends of Tesla Park. Though the draft concept designates about 500 acres around Tesla as limited recreation areas — meaning they could be completely off-limits to motorized use — the coalition remains adamantly opposed to any off-highway vehicle use, saying it would endanger habitats for native plant and animal species, and threaten culturally significant sites.

Off-road enthusiasts, however, were overwhelmingly pleased with the overall concept design, saying the expansion would provide more varied opportunities to enjoy their pastimes.

“It seems like a pretty diverse mix,” said motorcycle rider Tom Bueno, of Manteca, who visits Carnegie about once a week. “We definitely have a need for more space.”

Diana Mead, Northern California’s regional director of the California Off-Road Vehicle Association, called the proposal “as close to a dream concept” as she could have hoped for. Rider Betsy Fessler, of Campbell, said the new riding areas would allow her to spend more time recreating with her family.

“We’re excited about this expansion and the possibility of bringing the vehicles we use the most,” Fessler said. “It’s nice to see it’s going in that general direction.”

But avid hiker and Friends of Tesla Park supporter Garry Rodrigue, of Livermore, voiced his concerns about the damage the vehicles would do to the environment.

“I saw what they did to Carnegie (a nearby abandoned mining town); it’s an absolute mess,” Rodrigue said. “There’s a lot of history there. They can talk all they want, but they’ll destroy it. It’s a travesty.”

Friends of Tesla Park co-founder Celeste Garamendi, who owns a ranch near the expansion area, said the State Parks’ maps were “not based upon reality,” adding that off-highway usage would have a “devastating impact” on the area’s biodiversity.

“This place is so unique in that it has not only scenic beauty, but important biological features,” Garamendi said. “We should preserve it for future generations.”

The next step in the plan process will be completion of a draft environmental report sometime next year.

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